Complexation of monosubstituted benzenes and methanes by cyclotetrachromotropylene in aqueous solution: Substituent effects on π-π and Ch-π interactions

The stability constantsK of 11 complexes formed in aqueous solution between several monosubstituted benzenes (C₆H₅X) and methanes (CH₃X) as guests and cyclotetrachromotropylene as host were determined by proton NMR spectroscopy. Variations ofK with the substituent X are attributed to the electronic effect of X and the presence of C–H or aromatic bonds, if any, interacting with the host bonds.     

Highly effective and enantioselective α-amination of aldehydes promoted by chiral proline amide-thiourea bifunctional catalysts

A series of secondary amine-thiourea catalysts derived from l-proline and chiral diamine were prepared and successfully applied to the highly effective and enantioselective α-amination of unmodified aldehydes with various azodicarboxylates in excellent yields (up to 99%) and enantioselectivities (up to 99% ee) within a few minutes.     

Structure and Fluorescence Property of a 2D Bilayer Cd(Ⅱ) Coordination Polymer Induced by H-bonding and π-π Interaction

Solvothermal reactions of 4,4'-oxybis(benzoic acid) (H2oba) with 1,3-dipyridyl benzene (1,3-dpb) produced a two-dimensional (2D) cadmium(Ⅱ) coordination polymer {[Cd(oba)(dpb)]·H2O}n (1). The complex was characterized by elemental analysis, IR spectroscopy, and X-ray single-crystal diffraction. It crystallizes in the monoclinic system, space group C2/c with a = 13.6692(9), b = 25.9647(17), c = 8.7912(6) , α = 125.0370(10), γ = 2544.7(3)°, V = 2544.7(3) 3, C30H22N2O6Cd, Mr = 618.91, Dc =1.609 g/cm3, F(000) = 1248, μ = 0.904 mm-1 and Z = 4. The neighboring Cd(Ⅱ) ions are linked by oba2-anions and 1,3-dpb to form an infinitely 2D wavelike sheet, and two such 2D sheets are interlocked with each other by H-bonding to form a 2D → 2D structure. The adjacent two groups of interlocked structures are further linked to form a bilayer 2D supramolecular network by π-π interactions. In addition, the fluorescence property of 1 was also studied.     

Nuclephilic ring opening of epoxides promoted by multi-site phase-transfer catalyst:An efficient and eco-friendly route to synthesis of β-hydroxythiocyanate

A highly effective and mild protocol for ring opening of epoxides with NH4SCN in the presence of catalytic amount of a multisite phase-transfer catalyst,α,α′,α″-N-hexakis(triethylammoniummethylene chloride)-melamine,is developed.A variety ofβ-hydroxy thiocyanates as important intermediates in agricultural and pharmaceutical chemistry were obtained in high yields with excellent regioselectivity and in short reaction times.     

Enantioselective biomimetic transamination of α-keto acids catalyzed by H4-naphthalene-derived axially chiral biaryl pyridoxamines

Asymmetric biomimetic transamination is a highly attractive method for synthesis of chemically and biologically important chiral amino acids and chiral amines. Development of chiral pyridoxamines/pyridoxals is the key for the reaction. New axially chiral biaryl pyridoxamines based on H₄-naphathene skeleton have been developed. The pyridoxamines display good enantioselectivity and high catalytic activity in asymmetric biomimetic transamination of α-keto acids, affording various optically active unnatural amino acids in 61–98% yields with up to 91% ee’s.     

Synthesis of novel β-aminocyclobutanecarboxylic acid derivatives by a solvent-free aza-Michael addition and subsequent ring closure

Novel β-aminocyclobutanecarboxylic acid derivatives were prepared via a sequential solvent-free aza-Michael addition of benzophenone imine across 3-halopropylidenemalonates and base-induced ring closure. These highly substituted cyclobutanedicarboxylic acid derivatives were subjected to a reactivity study which demonstrated the tendency of these donor-acceptor substituted four-membered rings to be converted into their corresponding ring-opened products.     

Unprecedented π···π interaction between an aromatic ring and a pseudo-aromatic ring formed through intramolecular H-bonding in a bidentate Schiff base ligand: crystal structure and DFT calculations

A combination of a single crystal X-ray diffraction study and density functional theory calculations has been applied to a bidentate Schiff base compound to elucidate different cooperative non-covalent interactions involved in the stabilization of the keto form over the enol one in the solid state. The single crystal X-ray structure reveals a remarkable supramolecular assembly of the keto form through a cyclic hydrogen bonded dimeric motif. The most interesting feature in the supramolecular assembly is the formation of a 'dimer of dimer' motif by π···π, CH···π and N···O/O···O interactions in which the π···π interaction involving the aromatic phenyl ring and the intramolecularly hydrogen bonded pseudo-aromatic ring of the keto form lying just above or below the phenyl ring of the other dimer seems to be unprecedented. The optimized geometry of the hydrogen bonded dimeric motif of the keto form of the organic molecule has been obtained by DFT calculations and agrees very well with that found within the crystalline state. The X-ray crystallographic geometry of the 'dimer of dimer' has also been computed, which shows that in the HOMO, the π electrons are localized in the phenyl rings away from each other, while in the LUMO, there is a strong π-π interaction between the phenyl ring of one dimer with the pseudo-aromatic ring of another dimer with an energy estimated to be 7.95 kJ mol(-1). Therefore, on HOMO → LUMO excitation there is localization of π electrons in the central part of the complex moiety which plays a stabilizing role of the dimer of dimer motif in the solid state.     

Regio- and diastereoselective SN2′ or SN2″ reactions on chiral acetals of cyclic aldehydes promoted by PhCu,BF3

The regio- and diastereoselectivity of the addition of PhCu, BF₃ reagent on chiral acetals derived from several mono or dienic aldehydes was studied. It was found that monoethylenic acetals react regio- and diastereoselectively via an overall anti S_N2′ reaction. The regioselectivity observed with the dienic acetals seems to be strongly dependent on the nature of the acetal. In all cases the S_N2″reaction was the result of an anti process.     

Furan ring opening–indole ring closure: recyclization of 2-(2-aminophenyl)furans into 2-(2-oxoalkyl)indoles

The acid-catalyzed rearrangement of 5-alkyl-2-[2-(sulfonylamino)phenyl]furans into 2-(2-oxoalkyl)indoles is described. When the N-sulfonyl group in the starting compounds was displaced by an N-acyl group, the corresponding indoles were not formed under the same reaction conditions due to the in situ indole deacylation and decomposition. The presence of an alkyl group at the C5 position of the furan ring is also crucial for the efficiency of the process. The discussed rearrangement provides a simple and efficient approach to 2-(2-oxoalkyl)indoles.     

Highly homogeneous stereocontrolled construction of quaternary hydroxyesters by addition of dimethylzinc to α-ketoesters promoted by chiral perhydrobenzoxazines and B(OEt)3

A highly efficient enantioselective addition of Me(2)Zn to α-ketoesters, assisted by a chiral perhydro-1,3-benzoxazine ligand, is described. This novel catalytic system offers homogeneous elevated enantioselectivities in the preparation of α-hydroxyesters that bear a quaternary stereocenter, with a minor dependence on electronic and steric effects when aromatic, heteroaromatic, or aliphatic α-ketoesters are employed. The catalyst can be recovered and reused without loss of activity.     

Highly effective and enantioselective Michael addition of 4-hydroxycoumarin to α,β-unsaturated ketones promoted by simple chiral primary amine thiourea bifunctional catalysts

Highly asymmetric Michael addition of 4-hydroxycoumarin to α,β-unsaturated ketones promoted by chiral primary amine thiourea bifunctional catalysts was developed and a series of Michael adducts were obtained in excellent yields (up to 97%) and enantioselectivities (up to 95% ee). Optically pure S-warfarin was easily obtained in 99% ee after single recrystallization.     

Furan ring opening–indole ring closure: SnCl2-induced reductive transformation of difuryl(2-nitroaryl)methanes into 2-(2-acylvinyl)indoles

A simple and efficient method for the synthesis of 2-(2-acylvinyl)-3-(5-alkyl-2-furyl)indoles by reductive recyclization of bis(5-alkyl-2-furyl)(2-nitroaryl)methanes is reported. This transformation was carried out by heating the substrates with SnCl₂·2H₂O in ethanol. The intermediate nitrosoarene moiety interacted with the furan ring via electrophilic nitrogen attack onto the C(2) position of the furan ring. It was shown that the related bis(5-alkyl-2-thienyl)(2-nitroaryl)methanes under the same reaction conditions failed to undergo the analogous recyclization and were transformed into bis(5-alkyl-2-thienyl)(2-aminoaryl)methanes.     

Facile synthesis of α-methylidene-γ-butyrolactones: intramolecular Rauhut–Currier reaction promoted by chiral acid–base organocatalysts

The acid–base organocatalyzed intramolecular Rauhut–Currier (RC) reaction of the dienone enolates has been developed. The enantioselective RC process produces the highly functionalized α-methylidene-γ-butyrolactones as a single diastereomer with up to 98% ee.     

4 + 4] photodimerization of azaanthracenes in both solution and solid phase controlled by cation-π interactions

Regio- and stereoselective [4 + 4] photodimerization reactions of 1- and 2-azaanthracenes were performed in both methanol solution and solid phases to give anti-HT dimers in high yields. In these reactions, intermolecular cation-π interactions between the pyridinium cation and the benzene ring play a key role in preorientation prior to the photodimerization reactions.     

Efficient synthesis of β-amino alcohols by regioselective ring opening of epoxides with amines catalyzed by CuFe2O4 nanoparticles

A simple and efficient method has been developed for the synthesis of β-amino alcohols by regioselective ring opening of epoxides with amines in the presence of CuFe₂O₄ nanoparticles as a heterogeneous recyclable catalyst at room temperature in high yields.     

Intramolecular ring closure of α,β-epoxy sulfoxides with hydroxyl group: A novel synthesis of 2-acyl cyclic ethers and 3-keto cyclic ethers

Exo-trigonal-type intramolecular ring closure of the α,β-epoxy sulfoxides with hydroxyl group gave 2-acyl cyclic ethers (5, 6, and 13 membered rings) in good yields. In contrast to this, endo-trigonal-type ring closure of the α,β-epoxy sulfoxides was rather difficult.     

Benzoylation of benzene and substituted benzenes catalyzed by superacid ZrO_2:H_2SO_4

Superacid ZrO_2:H_2SO_4 showed high activity in Friedel-Crafts benzoylation of benzeneand substituted benzenes such an chlorobenzene,toluene and 1,3,5-trimethylbenzene.Benzophenonesin 90-100% yields were obtained with catalytic amount of superacid ZrO_2:H_2SO_4.The calcinationtemperature greatly influenced the acid strength and activity of the superacid ZrO_2:H_2SO_4.Thesuperacid has both Lewis and Bronsted acid sites.The reversibility of Friedel-Crafts benzoylation andtransacylation were observed over the superacid.The used superacid could be readily regenerated andshowed identical benzoylation activity to toluene.     

2D and 3D supramolecular assemblies of double cyclopalladated azobenzenes realized by C-H?Cl-Pd, π?π and C-H?π interactions

The double cyclopalladated complex with azobenzene, μ-[(E)-1,2-diphenyldiazene-C^2,8, N^1,2]-di-[chloro(dimethylsulfoxide)palladium(II)]; (DMSO)PdCl(μ-C₆H₄NNC₆H₄)(DMSO)PdCl (1) and its analogous complex with DMF as ancillary ligand, (DMF)PdCl(μ-C₆H₄NNC₆H₄)(DMF)PdCl; μ-[(E)-1,2-diphenyldiazene-C^2,8,N^1,2]-di-[chloro(dimethylformamide)palladium(II)] (2a) were synthesized and the function of cyclopalladated moiety in molecular assembling in the solid state is illustrated by their crystal packings. The polymorphism of 2a and 2b is discussed. The crystal structures reveal assemblies with molecular components self-organized by C-H?Cl-Pd hydrogen bonds, π?π, and C-H?π interactions. The double cyclopalladated complexes of azobenzene, with two Pd-Cl moieties participating in the hydrogen bond formation and π-conjugated system involved in the π?π or C-H?π interactions, represent a new class of building blocks for construction of solid state supramolecular assemblies.